The conviction of the utah doctor accused of murdering his wife. THREE OF martin MacNeill's adult daughters testified for the prosecution. Aditi roy sat down with the oldest daughter who may have pushed hardest to put her father behind bars. As for count one, murder one, guilty. Reporter: Gasps of joy from MICK shell MacNeill's family. Including her daughters, as the JURY FOUND martin MacNeill guilty of murdering his wife in 2007. Such a relief. Been finding for this so long. I never thought we would come to this day. I never thought it would make it to even trial. Reporter: Alexis summers waited for the moment for nearly seven years. Last year, alexis and her sister, rachel, held up pictures of their mother in court. She was taken away from me, from all of us. We're finally getting justice for her. Reporter: Alexis and rachel worked feverishly to reopen the investigation into their mother's death. The original medical examiner didn't find anything suspicious in her death. But they convinced the prosecutors and then a jury that her father gave mer mother precision medications that led to her drowning. Ever since the day that my mom died, I was concerned that my father killed her. Reporter: She said she once idolized her father. Now she will fight to keep him behind gbars. He was a con man. He victimized so many. Reporter: She says she'll have final words for him at his sentencing. It was something to see the reaction in the courtroom after the verdict was read.

This transcript has been automatically generated and may not be 100% accurate.

Utah doctor's mistress was the prosecution's last witness in his murder trial.

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